Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
1137 AM EST Fri Jan 25 2019

Valid Jan 25/1200 UTC thru Jan 29/0000 UTC

...See NOUS42 KWNO (ADMNFD) for the status of the upper air
ingest...

12Z Model Evaluation...with Preferences and Confidence
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...Overall Pattern across the CONUS...
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Preference: Non-NAM blend, weighted slightly more to the GFS
Confidence: Slightly above average

With a highly amplified pattern, model spread is generally low
relative to the typical amount in mid-winter, and confidence is
high in the synoptic pattern. Over the next few days, a broad and
amplified trough should be situated over the central and eastern
US. The greatest model variability is focused around the two
shortwaves producing the most significant precipitation in the
next couple days.

First, there is a shortwave currently pushing into Alaska that
will round the top of the West Coast ridge, and then dig sharply
toward the Gulf of Mexico by Sunday. The 00Z ECMWF and its
ensemble members continue to show the shortwave slower and more
amplified than most other deterministic models and NAEFS ensemble
members. The 12Z GFS did trend the shortwave slower, closer to the
00Z ECMWF scenario. However, a compromise in timing and strength
of the wave is preferred, as the ECMWF continues to represent the
slowest end of model spread and other than the amplified pattern
there is not an obvious blocking feature to slow the wave down
substantially.

The second shortwave will move across the North Pacific and reach
British Columbia by Saturday, eventually digging into the Midwest
late Sunday and into Monday. Ensemble sensitivity analysis
indicates that most of the model variability is related to the
latitudinal displacement of the wave as the timing is relatively
consistent (with minor differences). The 12Z NAM (and other recent
runs of the NAM) seem slightly too far north, as it is further
north than all but a few NAEFS+ECMWF ensemble members. A blend of
the other models leads to a reasonable consensus forecast.
However, a slight trend to the north has been noted on recent
cycles of both the GFS and ECMWF (the GFS is further north than
the ECMWF), so a blend that weights more strongly toward the GFS
is the preference.


Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml
500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml

Lamers